Chinese is Hieroglyphic so I think you can understand the difference from the word itself
了解——了:it means something had been down eg:我吃饭了
解—-know eg:解释(explaining.)
so maybe you can take it as I have understand it
as 明白
明—-it from 日 and 月 sun and moon means light,very bright
白—-means white
so from this word we can feel the feeling that when I am not very clear to see but suddenly some ray of light so it become clear .
there is a Chinese idioms also have the same meaning 恍然大悟(huang ran da wu )